Signal analyzer

ABSTRACT

A fiber length analyzer is disclosed that detects the various lengths of fibers present in a liquid medium and converts data representing these fiber lengths into a distribution related to the range and relative number of different fiber lengths present in the medium.

United States Patent Allinger et a1.

[ Dec. l7, 1974 1 SIGNAL ANALYZER 2,824,486 2/1958 Lawrance et al. 235/92 PC 2,851,596 9/1958 Hilton 235/92 TF [75] Inventors: Hubert Allmg"; Glen Gray; 3,783,247 1/1974 Klein et a1. 235/92 PC Robert S. Indre; Robert J. Kelly, all of Rochester, NY.

[73] Assignee: Eastman Kodak Company, Primary ExaminerGareth D. Shaw Rochester, NY. Assistant ExaminerJoseph M. Thesz, Jr. [22] Filed: Jan. 18, 1973 Attorney, Agent, or FzrmG. W. Grosser [21] Appl. No.: 324,634

52 us. c1..... 235/92 PC, 235/92 DN, 235/92 TF, [57] ABSTRACT 235/92 R, 324/71 CP, 356/102 [51] Int. Cl. G06m 11/04 A fiber length analyzer is disclosed that detects the [58] Field of Search 235/92 PC, 92 DN, 92 PB, various lengths of fibers present in a liquid medium 235/92 TF, 92 CV; 356/102; 324/71 CP and converts data representing these fiber lengths into a distribution related to the range and relative number [56] References Cited of different fiber lengths present in the medium.

UNITED STATES PATENTS 2,494,441 1/1950 Hillier 235/92 PB 3 Claims, 6 Drawing Figures DISPLAY U/V/T' l l 36\ cam/r52 U/V/T 42 5/ DELAY U/V/T FARf/CLE n PRE- PULSE nr i COMPUTER DETECTOR AMPL/F/Ef? AMPLIFIER GENERATOR D2 I V 33 J COMB/NAT- 2 22 24 2s 5% \5? DP/ l l 0P2 COUNTER- TIMER f u I 30 I I BINARY B/IVARY l OSC/LLATOR COUNTER ro-aco L I CONVERTER 0564055,

30t7 30b 30L 300' l L PATEHTED DEC] 71974 sum v1 or 4 /2 CURRENT SUPPLY F/GI PATENTEDBEEI 1 3; 855.455

SHEET 3 0F A VOLTS T/ME VOLTS SIGNAL ANALYZER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a signal analyzer for analyzing particles suspended in a medium, and more particularly, to a signal analyzer for determining a data distribution related to variations of selected particle characteristics.

2. Description of the Prior Art The sizing of small solids suspended in a liquid presents a number of obvious problems. One apparatus for measuring the size of particles suspended in a liquid is disclosed in U.S. Pat. No. 2,656,508, issued Oct. 20, 1953, to W. H. Coulter. This apparatus is arranged to pass a liquid conductor having particles suspended therein through an orifice and detect the modulation produced in a current flowing through the liquid in the orifice as a result of a particle entering the orifice. The size of the particle is determined by comparing the change in current magnitude caused by the unknown particle with that cuased by a particle of known size. In a related U.S. Pat. No. 3,259,842, issued July 5, 1966, to W. H. Coulter, et al., particle size is determined by a change in the amplitude of a voltage resulting from the passage of the particle through an orifice. In U.S. Pat. No. 3,529,239, issued Sept. 15, 1970, to R. B. Valley, et al., a particle counter arrangement of the same general type is utilized to provide electrical pulses respectively representative of the lengths of pulp fibers passing through an orifice, the duration of any given pulse being indicative of the length of its corresponding fiber. The pulse is amplified and clipped to provide a rectangular pulse of fixed amplitude. Each clipped pulse is then sorted according to its length by a wave generator which integrates the pulse so that the longer the pulse, the greater'its peak amplitude. The train of pulses is then applied to an amplitude discriminator which is arranged to detect all pulses greater than a given amplitude to thereby determine the number of fibers within the mix longer than a preselected length.

In U.S. Pat. No. 3,461,030, issued on Aug. 12, 1969, to M. A. Keyes, a sensing mechanism, an amplifier, a clipper circuit, and an integrator are utilized in a manner similar to that disclosed in the previously discussed Valley, et al., patent. In addition, the output of the integrator is delivered to a maximum value detector which converts an integrated pulse to a direct current voltage having substantially the same amplitude as the integrated pulse. An analog to digital converter, connected to receive the direct current voltage from the maximum value detector, derives a digital control signal indicative of the amplitude of the direct current voltage. The output of the analog to digital converter is delivered to a computer which automatically computes the average length of the fibers.

While the prior art apparatus provides useful data, it does not automatically provide the type of data desired where the range of variation in particle characteristics and the relative concentration of particles in a solution with different characteristics is important. For instance, information of this nature is important where it is desired to manufacture paper of uniform quality from a slurry containing fibers. Such information is also important where the level of quality of the paper being manufactured is of concern. In these situations, it is desirable that the relative concentration of fibers of different lengths and the range of fiber lengths be known in order to closely control the quality of the paper. One approach to obtaining data useful in controlling the relative concentration and range of fibers with different lengths is to determine a distribution representing the fiber lengths present in the slurry. The data generated by the prior art apparatus representing fibers exceeding a specified length or the average fiber length does not indicate either the range or the relative concentration of various fiber lengths present in the slurry. Further more, no prior art apparatus automatically provides data related to the relative concentration and range of fiber lengths in the medium.

SUMMARY OF THE INVENTION According to the invention, a signal analyzer for analyzing the nature of particles suspended in a liquid medium classifies variable duration signals representing a variable particle characteristic on the basis of signal duration. Signals with durations falling within each of a plurality of time intervals are counted to obtain data representing a distribution of the total range of variation in the particle characteristic being analyzed and the relative concentration of particles with differing characteristics in the medium. More specifically, the analyzer detects the presence of a particle and generates a signal with a duration that is proportional to the particle characteristic being analyzed, such as the length of the detected particle or the diameter of spherical particles. This signal is then converted into a digital code representing the signal duration. The occurrence of this digital code is recorded in one of a set of counters that each count the detection of particles with lengths falling within a different range of lengths, where length is the characteristic being analyzed. As particles with lengths in different ranges are detected, different counters are incremented, and the contents of the set of counters represent a distribution of the particle lengths present in the liquid medium. 7

The advantages of the invention are as follows: It provides a means for supplying information about the relative concentration and distribution of fiber lengths in a medium that is faster, more efficient, and more reliable than devices known in the prior art.

It is an object of the invention to provide novel apparatus for determining the variation of a characteristic of particles suspended in a liquid medium in a simple and economical manner.

Another object of the invention is to provide an apparatus for systematically classifying signals, representing particle characteristics, according to duration.

A more specific object of this invention is to provide an apparatus for generating data representing a distribution of the lengths of fibers suspended in a medium.

The present invention and its objects and its advantages will become more apparent in the detailed description of the illustrative embodiment presented below.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a sectional view of a conventional particle detector which serves as a particle detector in the illustrative embodiment of the invention;

FIG. 2 is a block diagram of a particle analyzing system in accordance with the illustrative embodiment of the invention;

FIG. 3 shows a waveform output of a pulse generator shown in FIG. 2;

FIG. 4 shows a waveform that is useful in describing the operation of the illustrative embodiment;

FIG. 5 is a more detailed block diagram of combinational logic and a counter unit shown in FIG. 2; and

FIG. 6 is a table showing a binary coded decimal representation of a number.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT Because particle analyzing devices are well known, the present description will be directed in particular to elements forming part of, or cooperating directly with, the present invention. Particle analyzer elements not specifically shown or described herein may take various forms well known to those skilled in the art.

Referring now to the drawings, wherein like numbers refer to similar parts, there is shown in FIG. 1 a particle detector 2 having an outer vessel 4 and an inner vessel 6 with a small orifice 8 mechanically and electrically coupling the fluid in the vessels together. Attached to the outer vessel 4 is an electrode 10 that is connected to a current supply 12. Inside the inner vessel 6 is a ground electrode 14, and a fluid withdrawal tube 16. The fluid in the vessels, in which the electrodes are submerged, is a saline solution 18 that has particles, such as fibers, suspended therein. The particle detector of FIG. 1 generally corresponds to the particle detector disclosed in the previously mentioned Coulter US. Pat. No. 2,656,508.

During the counting operation, a continuous and uniform pressure differential may be developed for a predetermined time through the orifice 8 whereby a known volume of saline solution 18 flows at a constant rate between the two vessels. The pressure differential is developed by a suction pump 19 connected to one end of the withdrawal tube 16. During the fluid flow, a signal is developed between the electrodes 10 and 14 that is a function of the electrical impedance of the saline solution 18 passing through the orifice 8. This impedance varies when a fiber in suspension in the solution flows through the orifice 8. The extent of the im pedance variation is proportional to the difference between the electrical conductivity of the saline solution 18 and the particle and also the volume of the particle effectively within the orifice. According to the basic operating principles of a "Coulter Counter," the amplitude of a fiber derived signal, such as S, in FIG. 2, is proportional to the volume of the particle in the orifice 8, and the duration of the signal is proportional to the duration of the particle residence in the orifice 8.

In accordance with the illustrative embodiment of the invention. a signal S, (FIG. 2), generated when the particle detector 2 detects a fiber. is amplified by preamplifier 22 to improve the signal-to-noise ratio for the signal. The output of the preamplifier 22 is also amplified by another amplifier 24 which brings the signal up to the necessary level for analysis. The signal is then shaped or squared by a pulse generator circuit 26, such as Schmidt trigger circuit, which converts the input signal into a waveform shown in FIG. 3. The pulse generator circuit 26 generates a high voltage level, or a l, at its output when the signal applied to its input reaches a predetermined trigger level, and the circuit will continue to generate a 1 until its input signal drops below the predetermined trigger level. When the signal applied to the input of the pulse generator circuit 26 drops below the predetermined trigger level, the circuit output becomes a 0.

The predetermined trigger level for the circuit 26 is determined by analyzing signals obtained when the solution 18 (FIG. 1) in the vessel 2 contains fibers typical of those to be measured. The detection of such fibers results in the generation of waveforms similar to the curve shown in FIG. 3, which indicates the relation be tween a fibers position in the orifice 8 and the signal obtained from the particle detector 2. The leading and trailing edges of the curve represent the situation where the fiber is entering or leaving the orifice, and a flat region of the curve L L represents the situation where the fiber is positioned in the orifice. The total length of the curve L L is related to the length of the detected fiber. The trigger level for the pulse generator circuit 26 is selected so that the circuit generates a 1 when its input reaches the level L and switches its output to 0 when the input signal decreases to the level L The result of this operation is a pulse (FIG. 3) whose duration T is substantially the same as the duration of the input signal (FIG. 4). In essence, the durations T of the pulses (FIG. 3) generated by the pulse generator circuit 26 are a function of the lengths of the detected fibers that result in the pulses being generated.

The duration T of the pulses generator output pulse (FIG. 3) will vary even when monosize fibers are being detected, since the velocity of the fluid passing through the orifice 8 (FIG. 1) varies from point to point in the orifice. The variation in the durations of the pulses generated by detected monosize fibers provides information relating to the velocity distribution of fiber lengths passing through the orifice. Mathematically, the following relationships exist between the pulse generator 26 (FIG. 2) output pulses and the length of the detected fibers. The mean pulse duration T of pulse generator output signals (FIG. 3) can be expressed as:

T= W ,7 L)

where L thickness of the orifice in mm Y= mean fiber length in mm reciprocal of the mean velocity Y of a fiber in mm/sec When monosize fibers are being analyzed, it is possible to determine W, and L, since 7 and Tare known. The variance in the reciprocal of the velocity W of a monosize fiber length distribution is represented by:

where a* variance in the reciprocal of the mean velocity 0% variance of the pulse width distribution Additionally, the variance of a fiber length distribution 0 can be obtained by:

Finally. a weighted mean fiber length 3? can be expressed as:

u x x2?- Consequently, the pulses generated by the pulse generator 26 (FIG. 2), in response to the detection of fibers, provide information that is related to the distribution of lengths of the detected fibers.

The pulses generated by the pulse generator 26, in response to the detection of fibers, are applied to a delay unit 28 (FIG. 2), and a counter-timer circuit 30. The counter-timer circuit determines the duration of the pulses generated by the pulse generator 26. When a pulse is generated by the pulse generator 26, the gate 30b is enabled for the duration of the pulse, resulting in the output of the constant frequenty oscillator 30a being applied to the counter 30c. Consequently, the counter 30c counts the number of sinewave cycles occurring while the gate 30b is enabled. When the pulse generated by the pulse generator 26 ends, the gate 30b is disabled, and the sinewave output of the oscillator 30a is no longer present as an input to the counter 300. At this point, the counter 30c contains a count representing the duration of the pulse generated by the pulse generator 26. In summary, the occurrence of a signal S, (FIG. 2), whose duration is related to the length of an individual fiber, results in the generation of a pulse that enables the gate 30b of the counter-timer 30 for an interval T (FIG. 3) related to the length of the fiber, and during this interval, constant frequency cycles generated by the oscillator 30a are counted by the counter 30c.

After the duration of the pulse generated by the pulse generator 26 (FIG. 2) has been measured by the counter 30c, a binary-to-BCD (binary coded decimal) converter 30d converts the contents of the counter 300 into a BCD number. Binary coded decimal coding is a system in which individual decimal digits are represented by a group of binary digits. A minimum of four binary digits is necessary to-represent a decimal digit.

For example, if a set of four bits is used to represent a decimal digit with the bit positions having weighted values of 8, 4, Li, then the number 765 would be represented by the three binary code words shown in FIG. 6. In essence, the binary code word b, represents units, the code word b represents tens, and the code word b represents hundreds. Each of these code words may be considered as the binary representation of one decimal decade where the code word b, for the first decade represents decimal units, the code word b for the second decade represents decimal tens, the code word b for the third decade represents hundreds, and so on to a fifth code word for a fifth decade which represents decimal ten-thousands. It will be noted that the binary-to- BCD converter 30d (FIG. 2) has a five-decade output and hence it can generate up to five BCD code words when the interval represented by the contents of the counter 300 is of a duration measureable in decimal tens of thousands.

Since it would not be practical, or particularly useful, to provide a counter for each of the possible codes in the five-decade output of the binary-to-BCD converter 30d, the overall range of outputs from the converter 30d is divided into sets of codes. For example, the output of the converter 30d could be divided into I5 sets, and I5 counters could be used to count the number of codes generated during an analysis that fall within each of these sets. The contents of these l5 counters could then be coverted into data representing I5 points on the fiber length distribution being determined. or the number of detected fiber lengths falling within each of the 15 length ranges.

Such a concentration of the binary-to-BC D converter 30d output results when these outputs are applied to the combinational logic 32, along with the pulse DP generated by the delay unit 28. It will be recalled that an output pulse from the pulse generator 28, whose duration is determined by the counter-timer circuit 30, is also applied to the delay unit 28. The delay DP, is sufficient to allow the counter-timer circuit 30 to determine the duration of such a pulse and convert it into a BCD code. At the time a BCD code representing the measured pulse duration appears at the output of the binary-to-BCD converter 30d, the delayed pulse DP appears as an output of the delay unit 28. The pulse DP. enables the combinational logic 32 which in turn translates the applied BCD code into a signal that is generated on one of its output lines 33. In the case where the output of the binary-to-BCD converter has been divided into 15 sets, a signal will be generated on one of the 15 lines on which the combinational logic 32 (FIG. 5) outputs appear, and a signal on this line indicates the particular one of these sets that includes the code value equal to the BCD code applied to the combinational logic. The combinational logic 32 may be any one of numerous types of wellknown logic decoders that translate an n bit input into a signal on one of m output lines.

More specifically, when the combinational logic 32 (FIG. 5) has 15 outputs, the BCD inputs to the decoding logic 38 in the combinational logic can be selected so that signals on the IS output lines are related to the duration of pulses generated by the pulse generator 26 (FIG. 2) in the following manner:

TABLE I Combinational Logic Output Line Pulse Durations Range in Microseconds Additionally, a range switch 37 (FIG. 5) is provided that changes the bit patterns to which the decoding logic 38 responds, and this allows the time range identified by signals on the combinational logic output lines to be changed. For instance, when the switch 37 is in one position, the bit patterns to which the decoding logic 38 responds result in the combinational logic generating output signals on the lines 33 that are related to the duration of pulses generated by the pulse generator 26 (FIG. 2) in the manner shown above in Table I. When the switch 37 is in a second position, the bit patterns to which the decoding logic 38 (FIG. 5) responds is changed, and the output signals generated on the lines 33 are related to the duration of the pulse generator output pulses in the following manner:

TABLE II Combinational Logic Output Line Pulse Durations Range in Microseconds l6 62 63 149 I50 239 240 459 460 829 830 I279 i280 i779 I780 2299 2300 2999 3000 3599 3600 4399 4400 5 I99 when the range switch 37 (FIG. 5) is in its first position,

the logic in the decoder that generates signals on line will only be enabled by those BCD code combina tions representing time intervals in the range of 16 to 37 microseconds. When the switch 37 is changed to its second position, a signal R is applied to the decoding logic 38 that results in logic that is responsive to BCD code combinations representing time intervals ranging from 16 to 62 microseconds generating signals on line 0. The signal R results in similar changes in the logic generating signals on the remaining lines, providing an increase from the time interval ranges of Table l to the range of time intervals shown in Table II.

After a BCD code combination has been decoded, the previously mentioned transfer pulse DP, (FIG. 2) generated by the delay unit 28 enables the gate 39 (FIG. in the combinational logic 32, resulting in the signal generated on one of the combinational logic output lines by this decoding being applied to a coder unit 34. This coder unit 34 responds to a signal on this given line by generating a unique code that is applied to counter address logic 40 in the counter unit 36. The counter address logic 40 responds by generating a signal that results in the contents of the counter C, associated with this line being incremented by one. At this point, the duration of the signal S, (FIG. 2), which is related to the length of a detected fiber. has been determined and a counter used to count the number of fibers having lengths in the range in which this fiber length falls has been incremented to reflect its detection. As additional fibers are detected. and the duration of the pulses generated as a result of the detection are determined, additional signals will be generated on various lines 33, resulting in the counters associated with each of these lines being incremented when a signal appears on its associated line. After a substantial number of fibers have been detected, the contents of the counters C, through C in the counter unit 36 will contain sufficient data for use in determining a distribution of detected fiber lengths. The counter unit 36 also contains a counter C that is incremented each time any of the other counters are incremented, and hence, it contains data representing the total number of fibers detected. The contents of the counter C are useful in determining if the system is operating properly and in determining when enough fibers have been detected to give an accurate distribution.

After the occurrence of each transfer pulse DP, transferring data to the coder unit 34 (FIG. 5), a second delay pulse DP, (FIG. 2) generated by the delay unit 28 is applied to the counter 300. This pulse DP, resets the counter 301: in preparation for timing the duration of the next pulse generated by the pulse generator 26 in response to the detection of another fiber.

The data stored in the counter unit 36 (FIG. 2) may be applied to a computer 42 which converts this data into actual points on a distribution of the detected fiber lengths. In addition, display capabilities 41 are provided which may comprise a cathode ray tube that converts the contents of the counters C, through C (FIG. 5) in the counter unit 36 into a histogram format, or digital readout tubes which display the number of counts in a given counter, or both.

The invention has been described in detail with particular reference to an illustrative embodiment thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

What is claimed is:

1. A signal analyzer for automatically generating data related to the distribution of lengths of fibers suspended in a liquid medium, said analyzer comprising:

detector means comprising means adapted for immersion in said medium and having an orifice for detecting the passage of fibers therethrough and for generating a train of detector output pulses in accordance therewith, the duration of said pulses being proportional to the length and velocity of said detected fibers through said orifice, and to the thickness of said orifice; I

means responsive to said detector output pulses for determining the time duration of each pulse, each of said durations being representative of weighted mean fiber length, and said means comprising oscillator means for generating a signal of predetermined frequency, gating means for controlling the transmission of said predetermined frequency signal in accordance with the duration of said output pulses, counter means for counting the number of cycles in each of the output signals of said gating means, and means for converting the output of said counter means into corresponding digital coded signals;

counter means responsive to said coded signals for counting the number of digital codes representing values within each of a plurality of value ranges; and

means for converting the counts in said counting means into data representing a distribution of lengths of fibers suspended in said liquid medium.

2. A signal analyzer according to claim 1 wherein said means responsive to said detector output pulses includes means for shaping said output pulses to a square waveshape of preselected amplitude, the duration of each square-shaped pulse being representative of the duration and the waveshape of the corresponding detector output pulse.

3. A signal analyzer according to claim 2 wherein said shaping means is adapted to respond to the leading and trailing edges of said detector output pulses to trigger at preselected levels thereof the leading and trailing edges, respectively, of said square-shaped pulses whereby the durations of said square-shaped pulses are caused to more closely represent actual times of fiber passage through said orifice.

I i l i 

1. A signal analyzer for automatically generating data related to the distribution of lengths of fibers suspended in a liquid medium, said analyzer comprising: detector means comprising means adapted for immersion in said medium and having an orifice for detecting the passage of fibers therethrough and for generating a train of detector output pulses in accordance therewith, the duration of said pulses being proportional to the length and velocity of said detected fibers through said orifice, and to the thickness of said orifice; means responsive to said detector output pulses for determining the time duration of each pulse, each of said durations being representative of weighted mean fiber length, and said means comprising oscillator means for generating a signal of predetermined frequency, gating means for controlling the transmission of said predetermined frequency signal in accordance with the duration of said output pulses, counter means for counting the number of cycles in each of the output signals of said gating means, and means for converting the output of said counter means into corresponding digital coded signals; counter means responsive to said coded signals for counting the number of digital codes representing values within each of a plurality of value ranges; and means for converting the counts in said counting means into data representing a distribution of lengths of fibers suspended in said liquid medium.
 2. A signal analyzer according to claim 1 wherein said means responsive to said detector output pulses includes means for shaping said output pulses to a square waveshape of preselected amplitude, the duration of each square-shaped pulse being representative of the duration and the waveshape of the corresponding detector output pulse.
 3. A signal analyzer according to claim 2 wherein said shaping means is adapted to respond to the leading and trailing edges of said detector output pulses to trigger at preselected levels thereof the leading and trailing edges, respectively, of said square-shaped pulses whereby the durations of sAid square-shaped pulses are caused to more closely represent actual times of fiber passage through said orifice. 